Complete the first half of the level (before you enter the blue door)then go back to the starting point.Look inside the pool of Radioactive waste and you should see a platform(if you flipped all the switches in the first half)

Walk across the platform towards the wall it leads to.The wall will open and you will have to defeat a serious of enemies.Explore the secret area more and you should find a exit door.Enter it and flip the switch(the stats will not appear).You will now be in an area called the Military Base.